Re: [tag] Current issue with "TA for properties"

[Stephen Green <stephen.green@documentengineeringservices.com>]

I've edited the section on property test assertions so that it now
reads as follows:



Test Assertions for Properties

Requirements addressed by test assertions may be related to specific
properties of a target. Assume there are specification requirements
that define under which conditions a widget qualifies as
“medium-size”. In other words, widgets do not come with a sticker that
makes this categorization obvious by announcing small / medium /
large. Instead, the size label is a property that is itself defined in
the widget specification and that is subject to verification, like any
other normative statement. In such a case, when writing test
assertions, it is not a good idea to consider this property as part of
the definition of the target category as in the case widget-TA101-1a
and widget-TA101-1b, because the category of a widget could not be
identified prior to doing any test on this widget.
Assume that the following requirement defines the “medium-size” property:
[requirement 104] “A widget that weighs between 100g and 300g and is
from 5 to 15 centimeters long in its longer dimension, is a
medium-size widget.”

There is a major distinction between requirement 104 and requirement 101:
requirement 101 uses “medium-size” as a prerequisite: its predicates
only concern widgets that are already established as medium-size.
requirement 104 defines how to qualify a test assertion as medium-sized.

The test assertions for requirement 104 can be written as:

TA id: widget-TA104-1
Normative Source: specification requirement 104
Target: widget
Predicate: [the widget] weighs between 100g and 300g.
Prescription Level: mandatory
Tag:normative_property = medium-sized

A tag, “normative_property = medium-sized” is assigned to convey that
the test assertion evaluation relates to the property ("medium-size").

TA id: widget-TA104-2
Normative Source: specification requirement 104
Target: widget
Predicate: [the widget] is from 5 to 15 centimeters long in its longer
dimension.
Prescription Level: mandatory
Tag:normative_property = medium-sized

The test assertions widget-TA104-1 and widget-TA104-2 will be used to
derive test cases that verify if the property "medium-size" applies to
some widget. A "false" outcome for their predicates is an indicator
that the medium-size property does not apply. It is not indicative of
a violation of the specification itself. Such test assertions are
called in this document "Property test assertions" to distinguish them
from test assertions that are used as indicators of conformance to a
specification. However, both types of test assertions are designed in
the same way, with a predicate that indicates whether or not a target
satisfies some feature or property.
There is no mention of the “medium-size” property in the predicates of
test assertions ‘widget-TA104-1’ and ‘widget-TA104-2’. This is because
this property is precisely what needs to be established by a test
suite containing test cases that are derived from these test
assertions. Only when a target (here a widget) evaluates to “true” for
these two test assertions, will it be considered medium-size. These
test assertions are only concerned with the nature of these tests, not
with how to interpret their outcome.




2009/5/21 Jacques R. Durand <JDurand@us.fujitsu.com>:
> Stephen:
>
> I was indeed the one most in favor of doing this prefixing of the prescription level :-\
> Realized that this does not work in general...
> The tag appears to be the most flexible way: adding a new TA element might open a new can of worms.
> I believe actually that it is good to not relate tightly the prescription level to the "intent" of the TA (here a property), which may change or may be more relevant to a combination of Tas.
> Let us discuss this next week.
>
> Jacques
>
> -----Original Message-----
> From: stephengreenubl@gmail.com [mailto:stephengreenubl@gmail.com] On Behalf Of Stephen Green
> Sent: Wednesday, May 20, 2009 12:21 PM
> To: TAG TC
> Subject: Re: [tag] Current issue with "TA for properties"
>
> I've not been quite convinced that there was a clear case for putting the property definition in the prescription level. I'm still a little uncertain about merely using a tag but it seems better than overloading presription level so unless anyone objects I will include this in another draft (along with some very minor rewording Jacques has suggested offlist).
>
> Best
>
> Steve
>
> 2009/5/20 Jacques R. Durand <JDurand@us.fujitsu.com>:
>> A medium technical issue with the current TAG draft:
>>
>> In section 3.3 "TA  for Properties":
>>
>> We recommend to mention the property ("medium-sized" ) in the
>> Prescription
>> element:
>>
>>
>> Prescription Level: medium-sized:mandatory
>>
>>
>> Because we want the prescription level to be associated with the
>> definition of this property.
>>
>>
>> [requirement 104] "A widget that weighs between 100g and 300g and is
>> from 5 to 15 centimeters long in its longer dimension, is a medium-size widget."
>>
>>
>>
>> Suggestion: instead of this, use a tag for expressing the association
>> of the TA to the property:
>>
>>
>> Prescription Level: mandatory
>>
>> Tag: normative_property = medium-sized
>>
>>
>> Rationale:
>>
>> - very close association between the Property and the Prescription
>> level (as currently suggested) is a bad idea: it seems to suggest that
>> the TA "widget-TA104-1" MUST evaluate to true (mandatory) for the
>> property to be verified.
>>
>> But that does not work if  [requirement 104] has "or" instead of "and" :
>>
>> [requirement 104] "A widget that weighs between 100g and 300g OR is
>> from 5 to 15 centimeters long in its longer dimension, is a medium-size widget."
>>
>> In that case we only want to indicate that the two TAs involved are
>> related to the definition of this property, nothing more, as you could
>> still satisfy the property even if you fail either TA. The
>> Prescription level should only reflect the wording in the requirement,
>> not be interpreted as a conformance statement.
>>
>>
>>
>> - a "normative property" should ultimately not be treated differently
>> from a conformance profile. In both cases we don't want the
>> Prescription level to be too closely associated with the profile or
>> property (which may require a more complex combination of TAs, to be
>> verified). Using a Tag is more appropriate for such a loose
>> association, whcih has simply the value of an annotation (grouping) with no other formal semantics.
>>
>> - The TA could be associated with several properties.
>>
>>
>>
>> Jacques
>
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